For the inter-process stabilization of the vertebral column from the posterior surgical approach, implants are applied in the form of one or several collaborating elements introduced into the inter-process space and linked with the spinous processes by means of ties in the form of a string or tape, or directly with the spinous process by means of screws, rings or other mechanical attachments. Known are also solutions in the form of elastic elements with ends specially profiled to fit the processes as well as instruments in the form of two plates embracing the lateral surfaces of the spinous processes with at least one of them linking the plates by a transverse part passing across the inter-process space.
Known from the patent description WO 99/40866 is an inter-process stabilizer for the fastening between two vertebral spinous processes. This stabilizer has the form of an elastic body consisting of two interconnected elastic parts as well as two anchoring parts in the form of arms provided with sharp protrusions fixed into the bones of the spinous processes between which the stabilizer is placed. The elastic parts of the stabilizer are shaped to a form close to at least one letter “U” or in one of the versions of the invention they have the form of a hollow cylinder with slits arranged along its axis.
An inconvenience of the described solution is the need to remove the supraspinous ligament in order to ensure a spot for the installation and fastening of the implant as well as an excessive lateral mobility of the neighboring processes. As a result of the fatigue of the material cyclically stressed during the postoperative exploitation, there also appears the risk of damage to the metallic implant.
Known from the patent description WO 99/42051 is an inter-process prosthesis consisting of an inter-process part as well as of integrated clasps jutting out in pairs on both its sides. These prosthesis clasps are considerably longer than the inter-process part in which at least one canal for the fastening of a tape linking the prosthesis with the processes is made. The prosthesis may also be placed in a fibrous pouch of the same shape with a tape constituting the implant-fastening element attached to it.
The described solution requires the separation of the soft tissues on both sides of the vertebral column as well as a rupture of the supraspinous ligament or its separation from the processes and its shifting aside during the installation of the implant, which constitutes considerable surgical invasiveness. Another inconvenience is also the absence of the possibility to regulate the distance between the clasps corresponding to the width of the spinous processes of the adjacent vertebrae as well as installation difficulties related to the setting of the prosthesis.
Known from the patent description PL354534 is the intervertebral implant consisting of a wedge provided with two incisures on opposite sides, intended for holding the spinous processes of two vertebrae. Each incisure is bordered by two protrusions between which the spinous process is located, and in each protrusion at least one hole is made for attaching the tie holding the wedge on the said spinous processes. The tie created from at least one tape grips a part of the surface of the spinous process, opposite to the bottom of the incisure and is tightened and subsequently blocked in a position joining the wedge permanently with the spinous processes.
An inconvenience of the application of the implant in accordance with this invention consists in the difficulties of the installation of the implant between the neighboring spinous processes, ensuring a correct arrangement stabilizing the bone-implant-tape system. A considerable invasiveness is caused by the necessity of a bilateral preparation of the soft tissues and shifting or cutting the supraspinous ligament and its fixation or reattachment after the installation of the implant.
Known from the patent description WO 03/099147 is a stabilizer constructed of two plates enveloping adjacent processes as well as a transverse link inserted between the processes and linking both plates at a definite distance from one another. The interior surfaces of the plates are provided with rings cutting into the lateral parts of the spinous processes when they approach one another along the link. One of the plates is set up on the link by means of an articulated joint and its installation with respect to the spinous processes is assured by a pin, while the other plate is fixed on the link by a processing screw.
A defect of this solution is the lack of a support for the spinous processes adapted to the inter-process space, not very stable fixation of the rings of the plates to the processes as well as a limitation of the movements of the patient and an unsatisfactory blockade of the stabilizer with respect to the spinal column.
Known from the patent description WO 2004/039243 is an implant adapted for the placement in between the spinous processes, consisting of a distance-keeping element and a means for adapting its height to the inter-process space. This implant consists of a body with a permanent wing as well as a roller upon which a distance-keeping element is set up in a rotary fashion as well as a wedge guide fastened with a screw. The distance-keeping element consists of two arms forming jointly a shape that is close to an oval and contain in between them a ball set up on a screw. This ball, when being screwed in, causes an extension of the arms of the distance-keeping element. An additional element may be another displaceable wing, also fixed on a roller beside the wedge guide.
A disadvantage of this solution is a complex design with a large number of constituent elements requiring an extensive invasive surgical access from both sides of the axis of the vertebral column. True, the design of the implant ensures the maintenance of the proper distance between the processes, but it can cause, especially when the patient bends down, excessive mobility and degradation of the bones loaded in the contact with the implant, thus limiting the time of the patient's stay in the sitting position.
Known from the patent description US 2004/0024458 is an inter-process implant in the form of a wedge with two furrows constituting the nests for the seating of the spinous processes. Between the furrows, in the central part of the wedge, there is a through hole the axis of which is parallel to the axes of the furrows. This hole constitutes from 10% to 30% of the total volume of the wedge, thanks to which the implant is susceptible to elastic deformation. In the lateral part of the wedge there are holes through which an elastic tape fixing the implant in the inter-process space is passed. A mobile element with a sharp edge, situated in a lateral niche of the wedge, serves the purpose of immobilizing the tightened tape.
The described complicated design forces the surgeon to cut or to separate extensively the soft tissues on both sides involved in fixing the spinous processes and to modify their surfaces to fit the shape of the surface of the implant. It requires also a rupture of the supraspinous ligament and carrying out complicated manipulations with a time-consuming tying up of the tension belt.
A modification of the above-described implant is the object of the invention in accordance with the patent description WO 02/071960. In this solution, two elastic tapes and two mechanisms fastening the tape are used. Apart from the inconveniences described above, the implant is characterized by a relatively large size and requires a wide surgical access arising also from the necessity of a bilateral fixation of the tensile tape.